magnetic deflection and scope-clocks - off the wall

[Opcom]

Not to be accused of unfinished projects, an update.

About ambition, all I have to do is remind myself how cool this will be if I can get it to work.

An obstacle has been the amplifier design. It has to be simple, and needs to behave like an op-amp. The basic design is about done, and the protection circuits were borrowed from Atari's schematics. The amp issue seems to have been solved by referring to "Electronics Now, OCT 1995, a powered subwoofer" and a simplfied version is attached as "XY deflection amp.pdf". it has errors, but just note the gain in the output stage and the op-amp running the show.

 - Update on deflection yokes is what today's post is about. I sort of expected this but was looking to provide info that would not require a difficult mechanical job from anyone wishing to try the project once it is eventully completed.

1. The amplifier schematc is done in CAD and I have ordered the parts for it. +/-170V will be the supply for this testing.

2. most importantly, I've dicovered some things about purpose-built vector display system yokes in comparison to TV anf computer monitor yokes. vector display yokes are a low inductance, very low in some cases. (of course they are not operated in a tuned circuit nor are they used to store energy as in a TV set) A TV set yoke has about 10mH inductance in the horizontal winding and about 40mH in the vertical winding. 10 is in the ballpark but at the high end, 40 is going to be impossible to drive with a +/-170V amplifier at 60KHz. Removing the ferrite core had a negligible effect on the inductance, maybe reduced it by 20%.

There is a guy on the www that has a "Space Duel" vector graphics video game. His vector deflection yoke died irrepairably. No one makes them any more. He has taken a TV chassis and yoke of some kind and rewound the yoke with 95 turns on each quadrant, that is 180 turns CT for X and the same for Y. The pictures of his monitor look fine. Even so, vector games do use a very slow drawing rate compared to the scopeclock.

An old military X-Y display was taken apart and the yoke was found to have 0.1mH inductance and 0.1 Ohm DCR. It looks like it has 10 turns per quadrant of relatively heavy wire.

What I have learned is what I should have seen at the beginning. The only thing that matters is ampere-turns. I could have one turn if I could push 100A through it.

Studying the military display yoke, it's wound with a few wires, and they are evenly placed so as to create a rather uniform field all the way around the CRT neck, OK all yokes are wound that way, but there are marked differences in exactly how they are wound. Regardles of energy storage needs, almost all of them have a ring of low-reluctance material around the outside. The purpose of this is to carry the lines of force efficiently around the outside of the coils where the force is not needed. Inside the circumference of the coils, the lines of force are used to deflect the beam inside the CRT. There's no need for an external field. The point is only efficiency.

The displays I am working with at this time have a 50-70 degree deflection angle. The first image shows different types of windings. Referring to file 1, An old type TV set yoke is a distributed winding like figure (d) and the XY display yoke from the military job is a semi-distributed winding like figure (e). A modern TV or computer yoke is a distributed winding designed for a greater degree of deflection angle, 90-110 degrees, and is like file 2. A semi-distributed winding is shown in file 3.

In file 1, the 'bars' of the windings are made of many turns each. It looks like bus, but it is not.

In file 2, the TV set yoke can be seen to have hundreds of turns in each quadrant. Two quadrants are visible, the vertical coils. In the video game guy's website, he removed all of that and wound the 92 turns each, it looks very spartan.

In file 3, this is the general appearance of the shape of just one set of windings of the military yoke. The CRT from that one is a 90 degree unit. It is not usable due to burns and I just got the display for the yoke. (It also has a nice 24V-to-16KV supply.). In the actual yoke, just imagine 10 turns of #20 on each side.

So, the first conclusion is that I will continue with the amplifier and use it for tests. It is capable of 10A, so should be fine, and is designed for a variable power supply of +/-35V to +/-170V.

The second conclusion is that I will have to take a standard (old) 50 or 70 degree yoke and disassemble it. I bough t one off ebay, and the kind and honest fellow neglected to inform me that the vertical winding was open, so this can be used for parts. After removing each coil, a little jig will have to be made around the coil, perhaps with brads on a wooden panel to get the size right, and then the coil removed. Next, 10-20 turns will be wound from #20 wire so that the winding is distributed like the X-Y military winding. This will be one quadrant and it ought to be a single layer 'pancake' coil.

It should then be driveable with an amplifier that anyone can duplicate and if everything is right, only +/-35 to +/-50V will be needed. That is in the range of most hobbyists. The project has to be duplicate-able by a hobbyist.

[Opcom]

here is file 3. it was very late last night when I quit.

[KC9LKE]

Pat:

Interesting topic! Sorry I haven’t taken the time to read all of the post. What exactly are your needs? Could you use an off the shelf monochrome X-Y display 19” or so? Driver boards and a yoke? In a past life, the place I was a tech at had at least a hundred X-Y’s setting on a shelf, with hundreds of driver boards in boxes. Atari, W-G, etc. I fixed them by the truck load and put them in stock. I’m probably living in the past and suggesting  something that has been sold off long ago, or now carries a big price, but if I can help I’ll ask to see what’s left.

Ted / KC9LKE   

[Opcom]

After a long time the project is still on. I stopped to work on the "COL Tucker" transmitter.

So, in answer, belatedly, yes I would like to find any existing electromagnetic XY displays, parts, boards, even the old arcade games that may be broken, etc. My funding is very limited right now but next year (almost there) should be better.

I am working with oscilloclock.com, the maker of the best-looking scope clocks, to create a hobbyist-compatible re-purposing of EM displays. Monochrome monitors would be welcome, esp. if I can just pick them up. It looks like we will rewind yokes for the experiments. Modern military vector displays I have dissected have yokes of relatively few turns of heavy wire, and are driven by rather simple solid state amplifiers. Example looks like 15-20 turns of #18 wire per yoke quadrant, a +/-40V supply, and about 10A amplifier capability.

We are just starting the project in earnest. I have to ship him some stuff, and we are going to collaborate making it a global project.

If anyone has a manual for the HP 1300A XY display or Wavetek 1901C scope, I am interested. Nothing complete is online and I'll ask the vendors.

[KA2DZT]

I have a HP 1208B xy display.  Can't find a manual for this one.  No high voltage and I can't find the problem. So it just sits on the self waiting to be scrapped.

Fred

[kg7bz]

Manuals Plus appears to have a service manual reprint for $20

http://www.manualsplus.com/manuals/AGILENT(HP)/1208B-H20

Also the manual for the HP 1300A

http://www.manualsplus.com/manuals/AGILENT(HP)/1300A

And the Wavetek 1901C

http://www.manualsplus.com/manuals/WAVETEK/1901C

August KG7BZ

[WBear2GCR]

Patrick, we must be brothers by different mothers!

I didn't recall posting to this thread, but a month back I bought one of those 'scope clock boards, they're being sold by another outfit under license from the dutchtronix fellow, inexpensive too...

Here's a picture!

No doubt something like a 8-12" XY monitor would be sweet!

[Opcom]

Looks like the sparkfun unit. They are mostly alike save the processor. It is exactly the reason to work at EM deflection. the bigger CRTs.

[WBear2GCR]

There's another guy who sells a board complete with PS and deflection amps, designed to run scope tubes, somewhat more expensive. Might be easier to apply?

           

[n1ps]

This is pretty cool...how did I miss this thread 3 years ago?  For $29....worth a try to play with one.  Are there any minimums as far as scope bandwidth?

[WBear2GCR]

I think the site mentions bandwidth, although I expect that in X/Y mode it's fairly free of bandwidth limitations. In other words I think this unit will work with an old Eico or Heath scope just fine.

A few years back this was a kit and more expensive, iirc.

                      _-_-

[KA2DZT]

Deflection plates of most any scope tube are good to about 80 mhz.

Fred

[Opcom]

I've tried the Sparkfun product on 2-5MHz scopes well. 5MHz makes a perfect display. On those much slower <2Mhz, you may see portions of the traces that ought to have been blanked but it is not annoying. depends on the scope.

There is a blanking output but it is usually the wrong polarity.

Beware that it ought not be just cap coupled to the cathode because when the capacitor charges upon scope power up it can destroy the DAC IC on the clock board, I have two popped ones here. A resistor to GND on the external side of the scope's blanking input (the kind of scope with the capacitively coupled to cathode blanking input) I'd recommend a vacuum tube voltage amplifier for isolation maybe a 6AU6 or anything, feed the blanking to the grid and take it inverted (properly) from the plate, to hook to the Z input of the scope.

[flintstone mop]

looks like expensive 'scope makes a good clock